Closing unit for an injection moulding machine

ABSTRACT

A closing unit of an injection molding machine includes a moveable mold mounting plate and a fixed mold mounting plate, a hydraulic pressure mechanism for building up a closing pressure, at least one column provided with an external profile, and at least one two-part nut which is provided with an internal profile and the halves of which are coupled in motionally opposite relationship. The at least one column in the closed condition of the two-part nut is lockable by a positively locking relationship between the internal profile and the external profile relative to the moveable mold mounting plate or relative to the pressure mechanism. There is also provided an electric drive for opening and closing the two-part nut.

The invention concerns a closing unit of an injection molding machinehaving the features of the classifying portion of claim 1.

An injection molding process generally begins with closure of theclosing unit, by the moveable mold mounting plate being moved towardsthe fixed mold mounting plate by a fast-action stroke device. Themoveable mold mounting plate is then locked with the pressure-applyingpiston member of a pressure mechanism and the pressure mechanism buildsup the closing pressure necessary for the injection process.

Frequently one or more columns are used for guiding the moveable moldmounting plate. In the case of an injection molding machine having onecolumn the pressure mechanism is often a hydraulic cylinder whose pistonexerts a pressure on the moveable mold mounting plate by way of thecolumn. The case of an injection molding machine having four columns,then also referred as bars, is also a familiar structure. Here thepressure mechanism is often in the form of a pressure cushion betweenthe mold mounting plates or at the ends of the bars. Those pressurecushions are also often hydraulic as high pressures have to be built upin a relatively short time.

The subject-matter of the invention is closing units of injectionmolding machines, in which after the working operation of thefast-action stroke, the columns are locked and the pressure mechanism issupported by way of the columns. In the foregoing examples on the onehand the columns are locked to the piston member of the pressuremechanism and on the other hand the bars are locked to the moveable moldmounting plate.

Locking actions of that kind are often implemented by two-part nutswhich embrace the columns of the closing unit. That applies both inregard to closing units having one column and also closing units havingfour columns. To be able to easily open and close the two-part nut it isadvantageous for the halves of the nuts to be mechanically coupled inmotionally opposite relationship to each other. Since, as in theabove-described examples, the devices necessary for the hydraulicarrangement are often already present there, it is standard procedure inthe state of the art to actuate both the fast-action stroke and also thetwo-part nuts hydraulically.

A disadvantage with hydraulic opening and closing of the nuts are arelatively long reaction time on the part of the hydraulic system and alack of precise positional detection of the two-part nuts. On the onehand, that means that time is lost in each injection molding process. Onthe other hand, that can lead to disturbances in operation or even todamage to the closing unit if the nut is not properly closed andconsequently locking of the column is incomplete.

The aim of the invention is to provide a closing unit having a lockingmechanism which does not suffer from the above-described disadvantages.

That object is attained by a closing unit having the features of claim1, that is to say in that there is provided an electric drive foropening and closing the halves of the nut.

Actuation and at the same time the above-mentioned coupling of thehalves of the nut, which occurs in motionally opposite relationship, canbe achieved in a mechanically particularly simple fashion by twoeccentrics which are connected to the electric drive and to a respectivehalf of the two-part nut.

In a further example there can be provided only one eccentric connectedto the electric drive and a half of the two-part nut. In that case thecoupling of the halves of the nut, which is in motionally oppositerelationship, can be implemented by a rotatably mounted rocker connectedat its ends to a respective half of the two-part nut. To avoid tiltingof that rocker mechanism there can particularly preferably also beprovided two such rockers.

To provide a compact structure, in a further embodiment of such aclosing unit having a plurality of bars it can be provided that twotwo-part nuts are opened and closed by an electric drive. In thatrespect it can be provided that a linkage couples the opening andclosing movements of the nuts.

Further advantages and details of the invention will be apparent fromthe Figures and the accompanying specific description. In the drawing:

FIG. 1 shows a cross-sectional view of a part of a closing unitaccording to the invention with one column,

FIG. 2 shows a diagrammatic side view of closing unit according to theinvention with four columns,

FIG. 3 a shows an opened two-part nut with electric drive, the halves ofthe nut being connected to the drive by way of two eccentrics,

FIG. 3 b shows the two-part nut from FIG. 3 a in the closed condition,

FIG. 4 a shows an open two-part nut with electric drive, wherein onlyone half is connected to the drive by way of an eccentric and couplingof the halves in motionally opposite relationship is achieved by tworocker mechanisms, and

FIG. 4 b shows the two-part nut of FIG. 4 a in the closed condition.

FIG. 1 shows a sectional view through the part of a closing unit 1 withone column 4, which has the pressure mechanism 14 and the moveable moldmounting plate 2. The internal profile 7 of the halves 12 of thetwo-part nut 6 (see also FIGS. 3 and 4) engages into the externalprofile 5 on the column 4. In that way the piston member 15 of thehydraulic pressure mechanism 14 can apply pressure to the moveable moldmounting plate 2. It will further be seen that the electric drive 8 inthis embodiment is fixed to the piston member 15 of the pressuremechanism 14 and actuates one half 12 of the divided nut 6 by way of aneccentric 9. In this embodiment the fast-action device 16 is in the formof a spindle mechanism in the interior of the column 4.

FIG. 2 shows an embodiment of a closing unit 1 having four columns, inwhich opening and closing of the halves 12 of two nuts 6 is effected byan electric drive 8 fixed to the moveable mold mounting plate 2. Herethe linkage 13 couples the opening and closing movements of the two-partnuts 6. In addition it is possible to see here the bars 4 with externalprofile 5, which pass through the moveable mold mounting plate 2. Thefast-action stroke device 16 as well as the pressure mechanism 15 withthe piston member 14 are also diagrammatically indicated. Theimplementation of such a pressure cushion is known to the man skilled inthe art.

FIGS. 1 and 2 respectively admittedly show horizontally closing closingunits. The invention however can also be used in vertical machines.

The two-part nut 6 shown in FIG. 3 a comprises two halves 12 which areeach provided with an internal profile 7. It is also possible to see twoeccentrics 9 by which the electric drive 8 actuates the two halves 12 ofthe two-part nut 6.

FIG. 3 b shows the same two-part nut 6 but in the closed condition.

FIG. 4 a shows a further embodiment with only one eccentric 9. Couplingof the two halves 12 of the two-part nut 6, which is in motionallyopposite relationship, is effected here by way of the two rotatablymounted rockers 10, the ends 11 of which are fixed to a respective oneof the halves 12 of the divided nut 6.

FIG. 4 b shows the divided nut from FIG. 4 a in the closed condition.

1. A closing unit (1) of an injection molding machine comprising a. amoveable mold mounting plate (2) and a fixed mold mounting plate (3), b.a hydraulic pressure mechanism (14) for building up a closing pressure,c. at least one column (4) provided with an external profile (5), and d.at least one two-part nut (6) which is provided with an internal profile(7) and the halves (12) of which are coupled in motionally oppositerelationship, wherein the at least one column (4) in the closedcondition of the two-part nut (6) is lockable by positively lockingrelationship between the internal profile (7) and the external profile(5) relative to the moveable mold mounting plate (2) or relative to thepressure mechanism (14), and wherein there is provided an electric drive(8) for opening and closing the two-part nut (6).
 2. A closing unit asset forth in claim 1, wherein there are provided two eccentrics (9)connected to the electric drive (8) and a respective half (12) of thetwo-part nut (6).
 3. A closing unit as set forth in claim 1, whereinthere is provided precisely one eccentric (9) connected to the electricdrive (8) and a half (12) of the two-part nut (6).
 4. A closing unit asset forth in claim 3, wherein there is provided at least one rotatablymounted rocker (10) having two ends (11), the ends (11) of which areconnected to a respective half (12) of the two-part nut (6).
 5. Aclosing unit as set forth in claim 4, wherein there are provided tworockers (10).
 6. A closing unit as set forth in claim 1 comprising afurther two-part nut (6) which is provided with an internal profile (7)and the halves (12) of which are coupled in motionally oppositerelationship, wherein a further column (4) in the closed condition ofthe further two-part nut (6) is lockable by positively lockingrelationship between the internal profile (7) and the external profile(5), wherein there is provided a linkage (13) which couples opening andclosing movements of the nuts (6).